Is my black molly pregnant?

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Aquarium Advice Apprentice
Oct 11, 2022
I recently got 4 black mollies from the pet store(3 females and 1 male) and one of the females has a bigger rounded belly than the rest, also she is losing some color in the belly area(unrelated) she is also nipping at the other fish….
Is she pregnant? Here are some pictures.


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If she has ever been in a tank with a male, she will be carrying sperm packets and can use these to fertilise eggs she is carrying at any time. So yes, she is probably gravid (pregnant). Gestation period is around 1 month but she is already fat so maybe 2 weeks.

If she doesn't give birth in 2 months, deworm the fish because they are regularly infested with round/ thread worms. If you need to deworm them, let me know and I will post instructions.

In the mean time, feed her well, do lots of big regular water changes and gravel clean the substrate. Have lots of plants in there, especially floating plants like Water Sprite (Ceratopteris thalictroides/ cornuta), and leave her in peace. If the male starts harassing her, put him in a breeding net or another tank for a few weeks.
Well, the male is nipping at her which I think is making her stressed and nipping at every fish… today, I noticed the male has a split dorsal fin, which I think she did. I have a large breeder box, should I put her in there this early? Will she prematurely give birth?
Don't move gravid females because you can stress them or kill the developing babies. The small breeding boxes also stress the females. You can move the male and that will sort out a lot of stress related issues. I prefer to keep common livebearers in single sex tanks so males don't harass females.

It is preferable not to move gravid (pregnant) fish because you can stress them and even damage the unborn fry. If you have to move gravid females, carefully catch them in a net and then use a plastic container to scoop the female and net up in some tank water. Move her (in the net in the bucket of water) to a new tank and then carefully pour her into the new tank.

If you move the female to a smaller aquarium that would stress her.

If you use completely new water in the new tank it would stress her. If you set up a new tank for her you should fill the new tank with water from her current tank, so the water is exactly the same.

If the new tank does not have any plants in it will stress her. Put some plants in with her. Water Sprite (Ceratopteris thalictroides/ cornuta) is the best plant for livebearers. It normally grows on the surface but can also be grown in the substrate where it grows into a lovely light green shrub.

If you don't have any live plants then add a heap of artificial plants to provide her with shelter when she goes into labour, and to give the fry somewhere to hide when they are born.

Make sure the new tank has an established filter in it so the water stays clean.
Do not put the female into a tank with males until at least 1 week after she has given birth otherwise the male/s will stress her out.

Try not to move the female for at least 1 week after she has given birth so she can heal up. If you have to move the female after she has given birth, use the method above for moving gravid females.

Most female mollies do not eat their young if the female is well fed and there are plants in the tank, but will eat them when they are confined to a small breeding trap.
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